1. Field of the Invention
The present invention relates to mobile wireless devices as used in personal and asset location systems. In particular, the present invention relates to a method and apparatus for utilizing the Global Position System (GPS) to locate objects over a large geographic region and to provide information or services related to a real time position of the object.
2. Description of the Related Art
With the advent of the Global Positioning System (GPS), there is growing demand for mobile devices that can locate and track children, the elderly, emergency situations, tourists, security, valuable assets, and the like. Devices built using conventional GPS receivers have been developed by a number of companies. These current generation devices have major limitations in terms of indoor penetration, power consumption, accuracy, and acquisition time.
To address the above issues new GPS processing architectures have evolved that utilize a combination of mobile GPS receivers and fixed GPS infrastructure communicating via wireless links. Systems with this architecture collect the majority of the data for location using the fixed infrastructure and, compared to traditional GPS, are able to offer large improvements in accuracy, indoor penetration, acquisition time, and power consumption. Thus far, such systems are based upon a fixed site GPS receiver that is physically located in the local vicinity of the mobile receiver and are therefore difficult to extend to broad coverage areas without a large proliferation of fixed site GPS receivers. Furthermore, such systems require a wireless link that provides communication in real-time and therefore such systems cannot take advantage of non real-time messaging systems such as paging networks.
Thus there is a need for a GPS processing architecture and device technology that provides the benefits of improved accuracy, indoor penetration, acquisition time, and power consumption and also offers the capability to function over large geographic coverage areas without requiring a fixed site GPS receiver in the local vicinity of the mobile device. Furthermore, to take advantage of broad coverage messaging systems, the architecture should have the ability to operate over a link which is not real-time, i.e. a link where there is significant and possibly unknown message latency.
In one embodiment of the invention, a method and apparatus is provided for performing timing synchronization in a mobile device. The method and apparatus include a wireless transceiver having a first oscillatory signal generator (OSG) and a Global Position System (GPS) receiver. The GPS receiver includes a second oscillatory signal generator coupled to a counter for receiving a first clock signal from the first OSG and a second clock signal from the second OSG. Additionally, a GPS signal processor is coupled to the counter. The counter provides a frequency offset signal between the first and second oscillatory signal generators to the GPS signal processor to adjust a pseudo-range model.
Further, in a second embodiment of the invention, a second method is provided for processing GPS signals in a mobile device during out-of-network coverage, where the mobile device includes the GPS receiver and a wireless transceiver. In particular, the method includes a) searching for a pilot tone of a cellular telephone for a first predetermined time by tuning a frequency of an oscillatory signal generator, and b) in an instance where the predetermined time lapses, fixing the frequency of the oscillatory signal generator. The method then c) searches for the GPS satellite signals for a second predetermined time, and d) in an instance where the second predetermined time lapses, the method returns to step (a).